43 results on '"Cuimei Wang"'
Search Results
2. Simulation Study of Enhancement-Mode InAlN/GaN HEMT with InGaN Cap Layer
- Author
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Wei Li, Xiaoliang Wang, Cuimei Wang, Jiang Lijuan, Zhanguo Wang, Quan Wang, Lin-Cheng Wei, Xiangang Xu, Chun Feng, Fengqi Liu, and Hongling Xiao
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Materials science ,business.industry ,Biomedical Engineering ,Mode (statistics) ,Optoelectronics ,General Materials Science ,Bioengineering ,General Chemistry ,High-electron-mobility transistor ,Condensed Matter Physics ,business ,Layer (electronics) - Published
- 2018
3. X-Band GaN High Electron Mobility Transistor Power Amplifier on 6H-SiC with 110 W Output Power
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Zhanguo Wang, Hongling Xiao, Chun Feng, Fengqi Liu, Quan Wang, Cuimei Wang, Jiang Lijuan, Xiaoliang Wang, and Xiangang Xu
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Materials science ,business.industry ,Amplifier ,Biomedical Engineering ,X band ,Optoelectronics ,General Materials Science ,Bioengineering ,General Chemistry ,High-electron-mobility transistor ,Condensed Matter Physics ,business ,Power (physics) - Published
- 2018
4. Optimization of growth and fabrication techniques to enhance the InGaN/GaN multiple quantum well solar cells performance
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Zhanguo Wang, Xiaoliang Wang, Cuimei Wang, Shiming Liu, Hongling Xiao, Weikun Ge, Quan Wang, and Kun Wang
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010302 applied physics ,Materials science ,Fabrication ,business.industry ,Multiple quantum ,Energy conversion efficiency ,02 engineering and technology ,Carrier lifetime ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Solar cell ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Current density ,Voltage - Abstract
Two structures of InGaN/GaN multiple quantum well solar cells are grown and fabricated in this work, which are 30 periods In0.14Ga0.86N/GaN (1.72 nm/4.14 nm, sample A) and In0.19Ga0.81N/GaN (2.76 nm/4.14 nm, sample B), respectively. The peak external quantum efficiency of sample A can reach over 60%, which is considered to be related with the longer carrier lifetime. The current density-voltage characteristics show that sample A exhibited an open-circuit voltage of 2.13 V, a short-circuit current density of 2.55 mA/cm2, a fill-factor of 65.7% and a conversion efficiency of 3.56%. Those indicators are among the best up to date as far as we know for InGaN/GaN solar cells.
- Published
- 2017
5. Asian Sports Power Competitive Strengths Contrastive Analysis
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Houyong Zhong and Cuimei Wang
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Power (social and political) ,Computational Mathematics ,Computer science ,General Materials Science ,General Chemistry ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Linguistics ,Contrastive analysis - Published
- 2016
6. Self-consistent simulation of two-dimensional electron gas characteristics of a novel (InxAl1-xN/AlN) MQWs/InN/GaN heterostructure
- Author
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Zhanguo Wang, Jiamin Gong, Wei Li, Xiaoliang Wang, Li Baiquan, Cuimei Wang, Haibo Yin, Junda Yan, and Quan Wang
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010302 applied physics ,Materials science ,business.industry ,chemistry.chemical_element ,Heterojunction ,02 engineering and technology ,Surfaces and Interfaces ,Self consistent ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Barrier layer ,chemistry ,0103 physical sciences ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,Nitride semiconductors ,business ,Layer (electronics) ,Indium ,Electronic properties - Abstract
In this paper, (InxAl1–xN/AlN) MQWs/InN/GaN heterostructure with a (InxAl1–xN/AlN) MQWs barrier layer and an InN channel layer is presented. The numerical calculations of 2DEG characteristics are made using a self-consistent solution of the Schrodinger and Poisson equations. The influence of (InxAl1–xN/AlN) MQWs and InN layer on band diagrams, 2DEG sheet density and carrier confinement are studied. The results show that an InN insert layer can improve the carrier-confinement ability without degrading the 2DEG sheet density in the heterostructure. The (InxAl1–xN/AlN) MQWs/InN/GaN heterostructure has both a larger 2DEG sheet density and better confinement of 2DEG than conventional InAlN/GaN and AlGaN/GaN heterojunctions. The 2DEG sheet density is as dramatically large as 3.85 × 1013 cm−2 with an AlN thickness of 1.5 nm, an In0.18Al0.82N thickness of 1.5 nm, an InN thickness of 0.5 nm, and pair number of 5. In addition, the influence of AlN thickness, InAlN thickness, indium content, and pair number on the 2DEG sheet density of the (InxAl1–xN/AlN) MQWs/InN/GaN heterostructure has been studied.
- Published
- 2016
7. Effects of a GaN cap layer on the reliability of AlGaN/GaN Schottky diodes
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Jiang Lijuan, Hongling Xiao, Quan Wang, Jiamin Gong, Li Baiquan, Enchao Peng, Haibo Yin, Chun Feng, He Kang, Xun Hou, Xiaoliang Wang, Hong Chen, Zhanguo Wang, Cuimei Wang, and Shenqi Qu
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Materials science ,business.industry ,Schottky barrier ,Schottky diode ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Stress (mechanics) ,Reverse leakage current ,Reliability (semiconductor) ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Thin film ,business ,Layer (electronics) ,Diode - Abstract
In this paper, AlGaN/GaN- and GaN/AlGaN/GaN-based Schottky barrier diodes (SBDs) were fabricated and studied for comparison. The recorded electrical characteristics of the devices show that the introduction of a GaN cap layer can evidently reduce the reverse leakage current and suppress the forward current decay of the devices. What is more important, the GaN/AlGaN/GaN-based SBDs are capable of greatly alleviating the unrecoverable degradation of the reverse characteristics, which was observed in the device without a GaN cap layer when the device was under long time reverse dc stress. Detailed analyses were discussed.
- Published
- 2015
8. Growth and characterization of AlGaN/AlN/GaN/AlGaN double heterojunction structures with AlGaN as buffer layers
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Hong Chen, Jiang Lijuan, Cuimei Wang, Xun Hou, Xiaoliang Wang, Hongling Xiao, Enchao Peng, Zhanguo Wang, Chun Feng, and Haibo Yin
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Materials science ,business.industry ,Heterojunction ,High-electron-mobility transistor ,Chemical vapor deposition ,Condensed Matter Physics ,Buffer (optical fiber) ,Inorganic Chemistry ,Full width at half maximum ,Materials Chemistry ,Sapphire ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Dislocation ,business - Abstract
High electron mobility transistors (HEMTs) structures with GaN, Al0.025Ga0.975N and Al0.04Ga0.96N high resistivity (HR) buffers were grown on sapphire by metal organic chemical vapor deposition (MOCVD). The structural and electrical properties of these three samples were investigated and compared. By increasing Al composition of AlGaN buffer, full width at half maximum (FWHM) values of (0002) and (10-12) x-ray rocking curves for buffer increase, indicating higher threading dislocation density. Room temperature noncontact Hall measurements were performed, and the measured 2DEG mobility was 1828 cm2/V s for GaN buffer, 1728 cm2/V s for Al0.025Ga0.975N buffer, and 1649 cm2/V s for Al0.04Ga0.96N buffer, respectively. Combining the theoretical calculation with the experiments, it was demonstrated that the decrease of mobility was attributed to higher dislocation density in sample with higher Al composition of AlGaN buffer. Devices were fabricated and it was found that the double heterojunction (DH) HEMT with Al0.025Ga0.975N buffer could effectively reduce the buffer leakage current.
- Published
- 2013
9. Numerical optimization of carrier confinement characteristics in (AlxGa1−xN/AlN)SLs/GaN heterostructures
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Haibo Yin, Cuimei Wang, Jiang Lijuan, Hongling Xiao, Hong Chen, Xiaoliang Wang, Jieqin Ding, and Chun Feng
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Condensed Matter::Materials Science ,Electron mobility ,Charge-carrier density ,Materials science ,Condensed matter physics ,Superlattice ,Heterojunction ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Saturation (magnetic) ,Induced polarization ,Electronic, Optical and Magnetic Materials - Abstract
We present numerical optimization of carrier confinement characteristics in (AlxGa1−xN/AlN)SLs/GaN heterostructures in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrodinger, Poisson, potential and charge balance equations. It is found that the sheet carrier density in GaN channel increases nearly linearly with the thickness of AlN although the whole thickness and equivalent Al composition of AlxGa1−xN/AlN superlattices (SLs) barrier are kept constant. This result leads to the carrier confinement capability approaches saturation with thicknesses of AlN greater than 0.6 nm. Furthermore, the influence of carrier concentration distribution on carrier mobility was discussed. Theoretical calculations indicate that the achievement of high sheet carrier density is a trade-off with mobility.
- Published
- 2012
10. Surface characterization of AlGaN grown on Si (111) substrates
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Xiaoliang Wang, Hong Chen, Chun Feng, Jiang Lijuan, Xu Pan, Haibo Yin, Cuimei Wang, and Hongling Xiao
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Materials science ,Morphology (linguistics) ,Scanning electron microscope ,Analytical chemistry ,Condensed Matter Physics ,Spectral line ,law.invention ,Inorganic Chemistry ,Crystal ,Optical microscope ,law ,Materials Chemistry ,Sapphire ,Field-effect transistor ,Molecular beam epitaxy - Abstract
Up to 500 nm thick crack-free Al 0.25 Ga 0.75 N and Al 0.32 Ga 0.68 N epilayers have been grown on Si (1 1 1) substrates. The surface morphology of samples was investigated by an optical microscope and a scanning electron microscope (SEM). Pits and shale-like surface structure have been observed. XRD rocking curve measurements indicate the crystal quality of samples. The analyses show that the Al source flux is an important factor in growing AlGaN on Si (1 1 1). The information from the Micro-Raman spectra supported that Al atoms are gathered at nearby areas of the pits originated from the AlN/Si (1 1 1) interface in the initial stage of AlGaN growth.
- Published
- 2011
11. Characteristics of high Al content AlGaN grown by pulsed atomic layer epitaxy
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Peng Jin, Xu Pan, Xiaoliang Wang, Cuimei Wang, Zhanguo Wang, Cuibai Yang, Weiying Wang, Wei Li, and Hongling Xiao
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Materials science ,Photoluminescence ,Phonon ,Analytical chemistry ,General Physics and Astronomy ,Gallium nitride ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Sapphire ,Atomic layer epitaxy ,symbols ,Light emission ,Spectroscopy ,Raman scattering - Abstract
Al 0.91 Ga 0.09 N epilayers have been obtained by pulsed atomic layer epitaxy (PALE) technique on sapphire (0 0 0 1) substrates. Deep ultraviolet (DUV) photoluminescence (PL) spectroscopy and Raman scattering spectrum have been employed to study the optical transitions in Al 0.91 Ga 0.09 N epilayers. We found the exciton-phonon interaction by fitting the asymmetric PL peak, in which the transverse optical phonon (TO) and the longitudinal optical (LO) phonon are the main contributor. The abnormal S-shaped temperature dependence of the PL band peak is less pronounced or has disappeared. Further analysis shows that there possibly exists a high density of deeper localized state (∼90 meV) in Al 0.91 Ga 0.09 N. The formation of these localized states provides a favorable condition for efficient light emission.
- Published
- 2011
12. Growth of GaN film on Si (111) substrate using AlN sandwich structure as buffer
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Cuimei Wang, Meng Wei, Xu Pan, Cuibai Yang, Hongling Xiao, and Xiaoliang Wang
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Materials science ,Silicon ,Aluminium nitride ,chemistry.chemical_element ,Mineralogy ,Gallium nitride ,Condensed Matter Physics ,Epitaxy ,Thermal expansion ,Strain energy ,Inorganic Chemistry ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Materials Chemistry ,symbols ,Thin film ,Composite material ,Raman scattering - Abstract
A single high temperature AlN (HT-AlN) buffer has been used to relieve the stress in the growth of GaN epilayers on Si (1 1 1) substrates, but the growth of crack-free GaN on Si is still difficult due to the large mismatch of the lattice and coefficient of thermal-expansion (CTE) between GaN and Si. In this paper, we report the growth of 1.2 μm thick crack-free GaN epilayers on 2 in. Si (1 1 1) substrates using the AlN sandwich structure as a buffer. The surface morphologies of the samples were observed using a microscope and AFM. Further analysis shows that the crack-free sample is closely correlated to the introduction of the AlN sandwich structure as the buffer. To better understand the relationship between the cracks and the stress, Raman scattering has been used to study the stress in the samples. The results indicate that the sandwich structure with top AlN and bottom AlN can more effectively accommodate the strain energy caused by CTE mismatch stress.
- Published
- 2011
13. Theoretical study on InxGa1−xN/GaN quantum dots solar cell
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Xiaoliang Wang, Cuibai Yang, Xun Hou, Qifeng Hou, Zhanguo Wang, Jinmin Li, Cuimei Wang, Haibo Yin, Hongling Xiao, and Qingwen Deng
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Theory of solar cells ,Materials science ,Condensed matter physics ,Heterojunction ,Quantum dot solar cell ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Polymer solar cell ,Electronic, Optical and Magnetic Materials ,law.invention ,Multiple exciton generation ,law ,Quantum dot ,Solar cell ,Electrical and Electronic Engineering ,Homojunction - Abstract
In this work, the structure of InxGa1−xN/GaN quantum dots solar cell is investigated by solving the Schrodinger equation in light of the Kronig–Penney model. Compared to p–n homojunction and heterojunction solar cells, the InxGa1−xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well.
- Published
- 2011
14. Effect of high temperature AlGaN buffer thickness on GaN Epilayer grown on Si(111) substrates
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Meng Wei, Zhanguo Wang, Cuibai Yang, Hongling Xiao, Xu Pan, Cuimei Wang, and Xiaoliang Wang
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Materials science ,business.industry ,Analytical chemistry ,Chemical vapor deposition ,Condensed Matter Physics ,Epitaxy ,Atomic and Molecular Physics, and Optics ,Buffer (optical fiber) ,Electronic, Optical and Magnetic Materials ,law.invention ,Stress (mechanics) ,Crystal ,Optical microscope ,Transmission electron microscopy ,law ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Layer (electronics) - Abstract
Crack-free GaN epitaxial layer was obtained through inserting 80 nm graded AlGaN buffer layer between GaN epilayer and high temperature AlN buffer on 2-in Si(111) substrates by metal organic chemical vapor deposition. This paper investigated the influence of AlGaN buffer thickness on the structural properties of the GaN epilayer. It was confirmed from the optical microscopy and scanning electronic microscopy that the graded AlGaN buffer with optimized thickness had a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed that AlGaN buffer with proper thickness could improve the crystal quality and surface morphology of the GaN film. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer by the insertion of graded AlGaN buffer.
- Published
- 2010
15. Growth temperature dependences of InN films grown by MOCVD
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Cuimei Wang, Jinmin Li, Jianping Li, Xiaobin Zhang, Junxue Ran, Cuibai Yang, Zhanguo Wang, Hongling Xiao, Guoxin Hu, and Xiaoliang Wang
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Morphology (linguistics) ,Materials science ,Analytical chemistry ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Chemical vapor deposition ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Metal ,Full width at half maximum ,visual_art ,visual_art.visual_art_medium ,Metalorganic vapour phase epitaxy ,Layer (electronics) - Abstract
We investigate the growth temperature dependences of InN films grown by metal organic chemical vapor deposition (MOCVD). Experimental results indicate that growth temperature has a strong effect on the surface morphology, crystalline quality and electrical properties of the InN layer. The increasing growth temperature broadened the v scan's full-width at half-maximum (FWHM) and roughened the surface morphology; whereas the electrical properties improved: As the temperature increased from 460 degrees C to 560 degrees C, room-temperature Hall mobility increased from 98 cm(2)/V s to nearly 800 cm(2)/V s and carrier concentration dropped from 5.29 x 10(19) cm (3) to 0.93 x 10(19) cm (3). The higher growth temperature resulted in more efficient cracking of NH3, which improved Hall mobility and decreased carrier concentration. (C) 2008 Elsevier B.V. All rights reserved.
- Published
- 2008
16. The effect of low temperature AlN interlayers on the growth of GaN epilayer on Si (111) by MOCVD
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Weijun Luo, L.W. Guo, Hongling Xiao, Xiaoliang Wang, Junxue Ran, Cuimei Wang, Jinmin Li, and Jianping Li
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Diffraction ,Morphology (linguistics) ,Materials science ,Silicon ,chemistry.chemical_element ,Chemical vapor deposition ,Substrate (electronics) ,Condensed Matter Physics ,law.invention ,Optical microscope ,chemistry ,law ,General Materials Science ,Metalorganic vapour phase epitaxy ,Electrical and Electronic Engineering ,Electron microscope ,Composite material - Abstract
Low temperature (LT) AlN interlayers were used to effectively reduce the tension stress and micro-cracks on the surface of the GaN epilayer grown on Si (111) substrate. Optical Microscopy (OM), Atomic Force Microscopy (AFM), Surface Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). In addition, wet etching method was used to evaluate the defect of the GaN epilayer. The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness, interlayer number and growth temperature of the LT AlN interlayer. With the optimized LT AlN interlayer structures, high quality GaN epilayers with a low crack density can be obtained. (C) 2008 Elsevier Ltd. All rights reserved.
- Published
- 2008
17. The influence of 1nm AlN interlayer on properties of the Al0.3Ga0.7N/AlN/GaN HEMT structure
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Baozhu Wang, L.W. Guo, Cuimei Wang, Weijun Luo, Xiaoyan Wang, Cebao Fang, Xiaoliang Wang, Guoxin Hu, Hongling Xiao, and Junxue Ran
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Electron mobility ,Materials science ,Condensed matter physics ,Hall effect ,X-ray crystallography ,General Engineering ,Heterojunction ,High-electron-mobility transistor ,Electron ,Metalorganic vapour phase epitaxy ,Polarization (waves) - Abstract
The sheet carrier concentrations, conduction band profiles and amount of free carriers in the barriers have been determined by solving coupled Schrodinger and Poisson equation self-consistently for coherently grown Al"0"."3Ga"0"."7N/GaN and Al"0"."3Ga"0"."7N/AlN/GaN structures on thick GaN. The Al"0"."3Ga"0"."7N/GaN heterojunction structures with and without 1nm AlN interlayer have been grown by MOCVD on sapphire substrate, the physical properties for these two structures have been investigated by various instruments such as Hall measurement and X-ray diffraction. By comparison of the theoretical and experimental results, we demonstrate that the sheet carrier concentration and the electrons mobility would be improved by the introduction of an AlN interlayer for Al"0"."3Ga"0"."7N/GaN structure. Mechanisms for the increasing of the sheet carrier concentration and the electrons mobility will be discussed in this paper.
- Published
- 2008
18. Photovoltaic effects in InGaN structures with p-n junctions
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Xiaobin Zhang, Hongling Xiao, Xiaoliang Wang, Guoxin Hu, Cuibai Yang, Xinhua Wang, Cuimei Wang, Jinmin Li, Jianping Li, and Junxue Ran
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Diffraction ,Indium nitride ,Band gap ,business.industry ,Schottky barrier ,Gallium nitride ,Surfaces and Interfaces ,Chemical vapor deposition ,Condensed Matter Physics ,medicine.disease_cause ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,medicine ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Electrical and Electronic Engineering ,business ,Ultraviolet - Abstract
InGaN photovoltaic structures with p-n junctions have been fabricated by metal organic chemical vapour deposition. Using double-crystal X-ray diffraction measurements, it was found that the room temperature band gaps of p-InGaN and n-InGaN films were 2.7 and 2.8 eV, respectively. Values of 3.4 x 10(-2) mA cm(-2) short-circuit current, 0.43 V open-circuit voltage and 0.57 fill factor have been achieved under ultraviolet illumination (360 nm), which were related to p-n junction connected back-to-back with a Schottky barrier and many defects of the p-InGaN film. 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- Published
- 2007
19. AlGaN/AlN/GaN/SiC HEMT structure with high mobility GaN thin layer as channel grown by MOCVD
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Hongling Xiao, Yiping Zeng, Zhanguo Wang, Jian Tang, Junxi Wang, Guoxin Hu, Zhiyong Ma, Jianping Li, Junxue Ran, Jinmin Li, Xiaoliang Wang, and Cuimei Wang
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Power gain ,Power-added efficiency ,Materials science ,business.industry ,Transconductance ,High-electron-mobility transistor ,Condensed Matter Physics ,Inorganic Chemistry ,Materials Chemistry ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,Current density ,Sheet resistance ,Power density - Abstract
Enhancement of the electrical properties in an AlGaN/GaN high electron mobility transistor (HEMT) structures was demonstrated by employing the combination of a high mobility GaN channel layer and an AlN interlayer. The structures were grown on 50 mm semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition (MOCVD). The room temperature (RT) two-dimensional electron gas (2DEG) mobility was as high as 2215 cm(2)/V s, with a 2DEG concentration of 1.044 x 10(13)cm(-2). The 50 mm HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with a resistance uniformity of 2.02%. The 0.35 Pin gate length HEMT devices based on this material structure, exhibited a maximum drain current density of 1300 mA/mm, a maximum extrinsic transconductance of 314 mS/mm, a current gain cut-off frequency of 28 GHz and a maximum oscillation frequency of 60 GHz. The maximum output power density of 4.10 W/mm was achieved at 8 GHz, with a power gain of 6.13 dB and a power added efficiency (PAE) of 33.6%. (c) 2006 Elsevier B.V. All rights reserved.
- Published
- 2007
20. Investigation of optical quenching of photoconductivity in high-resistivity GaN epilayer
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Jinmin Li, Xiaoyan Wang, Cuimei Wang, Cebao Fang, Guoxin Hu, Yiping Zeng, Junxi Wang, Zanguo Wang, Chengji Li, Jianping Li, Hongling Xiao, and Xiaoliang Wang
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Photocurrent ,Quenching (fluorescence) ,Materials science ,business.industry ,Band gap ,Photoconductivity ,Chemical vapor deposition ,Condensed Matter Physics ,Inorganic Chemistry ,Vacancy defect ,Materials Chemistry ,Sapphire ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business - Abstract
In undoped high-resistivity GaN epilayers grown by metalorganic chemical vapor deposition (MOCVD) on sapphire, deep levels are investigated by persistent photoconductivity (PPC) and optical quenching (OQ) of photoconductivity (PC) measurements. The PPC and OQ are studied by exciting the samples with two beams of radiation of various wavelengths and intensities. When the light wavelengths of 300 and 340 nm radiate the GaN epilayer, the photocurrent without any quenching effect is rapidly increased because the band gap transition only occurs. If the background light is 340 nm and the quenching light is 564 or 828 nm, the quenching of a small photocurrent generates but clearly. Two broad quenching bands that extend from 385 to 716 nm and from 723 to 1000 nm with a maximum at approximately 2.2 eV (566 nm) is observed. These quenching bands are attributed to hole trap level's existence in the GaN epilayer. We point out that the origin of the defects responsible for the optical quenching can be attributed to nitrogen antisite and/or gallium vacancy. (c) 2006 Elsevier B.V. All rights reserved.
- Published
- 2007
21. Influence of AlN interfacial layer on electrical properties of high-Al-content Al 0.45 Ga 0.55 N/GaN HEMT structure
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Zhanguo Wang, Jianping Li, Cuimei Wang, Guoxin Hu, Junxi Wang, and Xiaoliang Wang
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Materials science ,business.industry ,Doping ,General Physics and Astronomy ,Heterojunction ,Surfaces and Interfaces ,General Chemistry ,High-electron-mobility transistor ,Chemical vapor deposition ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Sapphire ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,Layer (electronics) ,Sheet resistance - Abstract
Unintentionally doped high-Al-content Al0.45Ga0.55N/GaN high electron mobility transistor (HEMT) structures with and without AlN interfacial layer were grown by metal-organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. The effects of AlN interfacial layer on the electrical properties were investigated. At 300 K, high two-dimensional electron gas (2DEG) density of 1.66 x 10(11) cm(-2) and high electron mobility of 1346 cm(2) V-1 s(-1) were obtained for the high Al content HEMT structure with a 1 nm AlN interfacial layer, consistent with the low average sheet resistance of 287 Omega/sq. The comparison of HEMT wafers with and without AlN interfacial layer shows that high Al content AlGaN/AlN/GaN heterostructures are potential in improving the electrical properties of HEMT structures and the device performances. (c) 2006 Elsevier B.V. All rights reserved.
- Published
- 2006
22. The effect of AlN growth time on the electrical properties of Al0.38Ga0.62N/AlN/GaN HEMT structures
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Xiaoliang Wang, Jianping Li, Cuimei Wang, Hongling Xiao, Junxi Wang, and Guoxin Hu
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Aluminium nitride ,Analytical chemistry ,Mineralogy ,Heterojunction ,Gallium nitride ,Chemical vapor deposition ,Condensed Matter Physics ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Sapphire ,Metalorganic vapour phase epitaxy ,Thin film ,Sheet resistance - Abstract
Al0.38Ga0.62N/AIN/GaN HEMT structures have been grown by metal-organic chemical vapor deposition (MOCVD) on 2-inch sapphire substrates. Samples with AIN growth time of 0s (without AIN interlayer), 12, 15, 18 and 24s are characterized and compared. The electrical properties of two-dimensional electron gas (2DEG) are improved by introducing AIN interlayers. The AIN growth time in the range of 12-18s, corresponding to the AIN thickness of 1-1.5 nm, is appropriate for the design of Al0.38Ga0.62N/AIN/GaN HEMT structures. The lowest sheet resistance of 277 Omega sq(-1) and highest room temperature 2DEG mobility of 1460 cm(2)V(-1) s(-1) are obtained on structure with AIN growth time of 12s. The structure with AIN growth time of 15s exhibits the highest 2DEG concentration of 1.59 x 10(13) cm(-2) and the smallest RMS surface roughness of 0.2 nm. (c) 2006 Elsevier B.V. All rights reserved.
- Published
- 2006
23. Deep levels in high resistivity GaN epilayers grown by MOCVD
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Jianping Li, Cuimei Wang, Chengji Li, Cebao Fang, Guoxin Hu, Xiaoliang Wang, Junxi Wang, and Chao Liu
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chemistry.chemical_compound ,High resistivity ,Materials science ,Deep level ,chemistry ,Electrical resistivity and conductivity ,Analytical chemistry ,Sapphire substrate ,Gallium nitride ,Metalorganic vapour phase epitaxy ,Chemical vapor deposition ,Condensed Matter Physics - Abstract
Undoped high resistivity (HR) GaN epilayers were grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Thermally stimulated current (TSC) and resistivity measurements have been carried out to investigate deep level traps. Deep levels with activation energies of 1.06eV and 0.85eV were measured in sample 1. Gaussian fitting of TSC spectra showed five deep levels in different samples. (c) 2006 WILEY VCH Vertag GmbH & Co. KGaA, Weinheim
- Published
- 2006
24. Room temperature mobility above 2100 cm 2 /Vs in Al 0.3 Ga 0.7 N/AlN/GaN heterostructures grown on sapphire substrates by MOCVD
- Author
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Junxi Wang, Guoxin Hu, Cuimei Wang, Xiaoliang Wang, and Jianping Li
- Subjects
Materials science ,business.industry ,Sapphire ,Optoelectronics ,Heterojunction ,High-electron-mobility transistor ,Metalorganic vapour phase epitaxy ,Chemical vapor deposition ,Condensed Matter Physics ,business ,Fermi gas ,Sheet resistance ,Molecular beam epitaxy - Abstract
Al0.3Ga0.7N/AlN/GaN HEMT structures with significantly high mobility have been grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. At room temperature (RT) a Hall mobility of 2104 cm(2)/Vs and a two-dimensional electron gas (2DEG) density of 1.1x10(13) cm(-2) are achieved, corresponding to a sheet resistance of 277.8 Omega/sq. The elimination of V-shaped defects were observed on Al0.3Ga0.7N/AlN/GaN HEMT structures and correlated with the increase of 2DEG mobility. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim.
- Published
- 2006
25. Influence of Al content on electrical and structural properties of Si‐doped Al x Ga 1–x N/GaN HEMT structures
- Author
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Junxi Wang, Guoxin Hu, Xiaoliang Wang, Cuimei Wang, and Jianping Li
- Subjects
Materials science ,Analytical chemistry ,Heterojunction ,Nanotechnology ,High-electron-mobility transistor ,Chemical vapor deposition ,Condensed Matter Physics ,Mole fraction ,chemistry.chemical_compound ,chemistry ,Aluminium oxide ,Sapphire ,Metalorganic vapour phase epitaxy ,Sheet resistance - Abstract
Improved electrical properties of AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures grown by metalorganic chemical vapor deposition (MOCVD) were achieved through increasing the Al mole fraction in the AlGaN barrier layers. An average sheet resistance of 326.6 Omega/sq and a good resistance uniformity of 98% were obtained for a 2-inch Al0.38Ga0 62N/GaN HEMT structure. The surface morphology of AlxGa1-xN/GaN HEMT structures strongly correlates with the Al content. More defects were formed with increasing Al content due to the increase of tensile strain, which limits further reduction of the sheet resistance. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim.
- Published
- 2006
26. Growth of GaN nanowires through nitridation Ga2O3 films deposited by electrophoresis
- Author
-
Huizhao Zhuang, Chengshan Xue, Cuimei Wang, and Li Yang
- Subjects
Materials science ,Fabrication ,Scanning electron microscope ,business.industry ,Nanowire ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Crystallography ,Electrophoresis ,Transmission electron microscopy ,Optoelectronics ,business ,Single crystal ,Nitriding ,Wurtzite crystal structure - Abstract
Synthesizing hexagonal wurtzite GaN nanowires involves nitriding Ga2O3 films, which deposited on GaAs(1 1 0) substrates with electrophoresis. The cylindrical structures of GaN nanowires with the diameters ranging from 40 to 200 nm and lengths up to over 100 μm have been obtained. Scanning electron microscopy (SEM) images showed the morphologies of the one-dimensional single crystal materials containing straight and curved nanowires. GaN spherical crystals attached to the fibers with diameters about 600 nm were detected for the first time. The synthesis of one-dimensional GaN nanowires can be achieved without assistance of a template of a catalyst.
- Published
- 2003
27. Formation of high quality gallium nitride thin films on Ga-diffused Si(1 1 1) substrate
- Author
-
Li Yang, Huizhao Zhuang, Cuimei Wang, Qinqin Wei, and Chengshan Xue
- Subjects
Materials science ,Photoluminescence ,Analytical chemistry ,General Physics and Astronomy ,Gallium nitride ,Surfaces and Interfaces ,General Chemistry ,Substrate (electronics) ,Sputter deposition ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Crystallography ,chemistry ,X-ray photoelectron spectroscopy ,Transmission electron microscopy ,Cavity magnetron ,Thin film - Abstract
High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(1 1 1) substrates through ammoniating Ga 2 O 3 thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 A. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga 2 O 3 and NH 3 on the Ga-diffused Si(1 1 1) substrates.
- Published
- 2003
28. AlGaN/GaN/InGaN/GaN DH‐HEMTs structure with an AlN interlayer grown by MOCVD
- Author
-
Cuimei Wang, Hongling Xiao, Jian Tang, Jinmin Li, Guoxin Hu, Xiaoyan Wang, Junxue Ran, and Xiaoliang Wang
- Subjects
Materials science ,business.industry ,Hall effect ,Optoelectronics ,Heterojunction ,Surface finish ,Metalorganic vapour phase epitaxy ,Dislocation ,Condensed Matter Physics ,business ,Fermi gas ,Layer (electronics) ,Sheet resistance - Abstract
A novel AlGaN/GaN/GaN/GaN double heterojunction high electron mobility transistors (DH-HEMTS) structure with an AlN interlayer on sapphire substrate has been grown by MOCVD. The structure featured a 6-10 nm In0.1Ga0.9N layer inserted between the GaN channel and GaN buffer. And wer also inserted one ultrathin. AlN interlayer into the Al/GaN/GaN interface, which significantly enhanced the mobility of two-dimensional electron gas (2DEG) existed in the GaN channel. AFM result of this structure shows a good surface morphology and a low dislocation density, with the root-mean-square roughness (RMS) of 0.196 nm for a scan area of 5 mu m x 5 mu m. Temperature dependent Hall measurement was performed on this sample, and a mobility as high as 1950 cm(2)/Vs at room temperature (RT) was obtained. The sheet carrier density was 9.89 x10(12) cm(2), and average sheet resistance of 327 Omega/sq was achieved. The mobility obtained in this paper is about 50% higher than other results of similar structures which have been reported. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- Published
- 2008
29. MOCVD-grown high-mobility Al0.3Ga0.7N/AlN/GaN HEMT structure on sapphire substrate
- Author
-
Hongling Xiao, Cebao Fang, Guoxin Hu, Cuimei Wang, Jianping Li, Junxue Ran, Jinmin Li, Xiaoliang Wang, Zhanguo Wang, and Junxi Wang
- Subjects
Inorganic Chemistry ,Barrier layer ,Electron mobility ,Chemistry ,Transmission electron microscopy ,Materials Chemistry ,Analytical chemistry ,Wafer ,Metalorganic vapour phase epitaxy ,High-electron-mobility transistor ,Chemical vapor deposition ,Condensed Matter Physics ,Sheet resistance - Abstract
High-mobility Al0.3Ga0.7N/AlN/GaN high electron mobility transistors (HEMT) structure has been grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrate. Electron mobility of 2185 cm(2)/V s at room temperature and 15,400 cm(2)/V s at 80 K with 2DEG density of 1.1 X 10(13) cm(-2) are achieved. The corresponding sheet resistance of the HEMT wafer is 258.7 Omega/sq. The AlN interfacial layer between the GaN buffer and the AlGaN barrier layer reduces the alloy disorder scattering. X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements have been conducted, and confirmed that the wafer has a high crystal quality. (c) 2006 Elsevier B.V. All rights reserved.
- Published
- 2007
30. The influence of Fe doping on the surface topography of GaN epitaxial material
- Author
-
Cui Lei, Haibo Yin, Quan Wang, Bo Zhang, Jiamin Gong, Chun Feng, Cuimei Wang, Jiang Lijuan, Li Baiquan, Hongling Xiao, Xiaoliang Wang, and Zhanguo Wang
- Subjects
Surface (mathematics) ,Epitaxial material ,Materials science ,business.industry ,Doping ,High-electron-mobility transistor ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Optics ,High resistivity ,Electrical resistivity and conductivity ,Materials Chemistry ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Growth rate ,Electrical and Electronic Engineering ,business - Abstract
Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 1019 cm−3. High resistivity GaN epitaxial material which is 1 × 109 Ωcm is achieved.
- Published
- 2015
31. Analysis of GaN cap layer effecting on critical voltage for electrical degradation of AlGaN/GaN HEMT
- Author
-
He Kang, Junda Yan, Shenqi Qu, Chun Feng, Hongling Xiao, Jiang Lijuan, Xun Hou, Cuimei Wang, Haibo Yin, Hong Chen, Xiaoliang Wang, Zhanguo Wang, and Enchao Peng
- Subjects
Materials science ,business.industry ,Transistor ,High voltage ,High-electron-mobility transistor ,Condensed Matter Physics ,Critical value ,Electronic, Optical and Magnetic Materials ,law.invention ,Barrier layer ,law ,Electric field ,Optoelectronics ,business ,Instrumentation ,Layer (electronics) ,Voltage - Abstract
We present calculation of critical voltage for AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layer. The calculation includes mechanical stress and relaxable energy in the GaN/AlGaN barrier layer. Under high voltage conditions, the high electric field results in an increase in stored relaxable energy. If this exceeds a critical value, crystallographic defects are formed. This degra- dation mechanism is voltage driven and characterized by a critical voltage beyond which non-reversible degradation takes place. The dependence of the GaN cap layer's thickness on the critical voltage has been discussed. The calculated results indicate that thicker GaN cap layer results in higher critical voltage.
- Published
- 2014
32. Two-dimensional electron and hole gases in InxGa1−xN/AlyGa1−yN/GaN heterostructure for enhancement mode operation
- Author
-
Shenqi Qu, Chun Feng, Hongling Xiao, Quan Wang, Cuimei Wang, Enchao Peng, He Kang, Zhanguo Wang, Haibo Yin, Junda Yan, Li Baiquan, Xun Hou, Xiaoliang Wang, and Jiang Lijuan
- Subjects
Barrier layer ,Electron mobility ,Materials science ,Depletion region ,Condensed matter physics ,Electric field ,Doping ,Analytical chemistry ,General Physics and Astronomy ,Heterojunction ,Electron ,Fermi gas - Abstract
In this paper, a numerical study of In x Ga1 − x N/Al y Ga1 − y N/GaN heterostructure is presented. The dependence of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) sheet densities on variables, such as In x Ga1 − x N layer thickness and In content, and Al y Ga1 − y N barrier layer thickness and Al content, are systematically investigated. The effect of P-type doping in In x Ga1 − x N on 2DEG and 2DHG sheet densities in this heterostructure is also studied. It is shown that the strong reverse electric field in In x Ga1 − x N cap layer contributes to the depletion of 2DEG at the Al y Ga1- y N/GaN interface. When In x Ga1 − x N layer thickness and In content increases, 2DEG sheet density decreases significantly. P-type doping shows less influence on 2DEG compared to the polarization electric field in In x Ga1 − x N layer. In addition, there exist critical values for all the variables beyond which 2DHG appears at the interface of In x Ga1 − x N/Al y Ga1 − y N. Once 2DHG appears, it will prevent 2DEG from being further depleted. With proper design of Al y Ga1 − y N layer, the coexistence of 2DEG and 2DHG in In x Ga1 − x N/Al y Ga1 − y N/GaN structure can be avoided, showing that this structure has great potential in the fabrication of enhancement mode (E-mode) high electron mobility transistors.
- Published
- 2014
33. Analysis of transconductance characteristic of AlGaN/GaN HEMTs with graded AlGaN layer
- Author
-
Jiang Lijuan, Zhanguo Wang, Chun Feng, Hongling Xiao, Enchao Peng, Shenqi Qu, He Kang, Haibo Yin, Hong Chen, Cuimei Wang, Xiaoliang Wang, and Xun Hou
- Subjects
Materials science ,Phonon ,business.industry ,Transconductance ,Transistor ,Nanotechnology ,Algan gan ,Surface finish ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Optoelectronics ,business ,High electron ,Instrumentation ,Layer (electronics) - Abstract
A theoretical study of transconductance characteristics ( g m − V gs profile) of AlGaN/GaN high electron mobility transistors (HEMTs) with a graded AlGaN layer is given in this paper. The calculations were made using a self-consistent solution of the Schrodinger-Poisson equations and an AlGaN/GaN HEMTs numerical device model. Transconductance characteristics of the devices are discussed while the thickness and Al composition of the graded AlGaN layer are optimized. It is found that graded AlGaN layer structure can tailor device’s g m − V gs profile by improving polar optical phonon mobility and interface roughness mobility. Good agreement is obtained between the theoretical calculations and experimental measurements over the full range of applied gate bias.
- Published
- 2014
34. Enhanced performance of InGaN/GaN multiple quantum well solar cells with patterned sapphire substrate
- Author
-
Jieqin Ding, Zhanguo Wang, Xun Hou, Zhidong Li, Xiaoliang Wang, Qingwen Deng, Hongling Xiao, Cuimei Wang, and Liang Jing
- Subjects
Materials science ,integumentary system ,Scattering ,business.industry ,Multiple quantum ,food and beverages ,Quantum dot solar cell ,Edge (geometry) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,stomatognathic diseases ,law ,Solar cell ,Materials Chemistry ,Sapphire ,Optoelectronics ,Sapphire substrate ,Electrical and Electronic Engineering ,business ,Absorption (electromagnetic radiation) - Abstract
In this paper, the enhanced performance of InGaN/GaN multiple quantum well solar cells grown on patterned sapphire substrates (PSS) was demonstrated. The short-circuit current (Jsc) density of the solar cell grown on PSS showed an improvement of 60%, compared to that of solar cells grown on conventional sapphire substrate. The improved performance is primarily due to the reduction of edge dislocations and the increased light absorption path by the scattering from the textured surface of the PSS. It shows that the patterned sapphire technology can effectively alleviate the problem of high-density dislocations and low Jsc caused by thinner absorption layers of the InGaN based solar cell, and it is promising to improve the efficiency of the solar cell.
- Published
- 2013
35. Pyroelectric properties of sol?gel derived lithium tantalite thin films
- Author
-
Ming-Cheng Kao, Ying-Chung Chen, Cuimei Wang, and Hone-Zern Chen
- Subjects
Materials science ,business.industry ,Tantalite ,chemistry.chemical_element ,Dielectric ,engineering.material ,Specific detectivity ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Pyroelectricity ,chemistry ,engineering ,Optoelectronics ,Figure of merit ,Lithium ,Infrared detector ,Electrical and Electronic Engineering ,Thin film ,business - Abstract
Lithium tantalite (LiTaO3) thin films (∼0.5 μm ) have been successfully deposited on Pt (111)/ SiO 2 / Si (1 0 0) substrates by means of sol–gel spin-coating technology. Figures of merit for infrared detector were studied for the LiTaO3 thin films. There exists high figures of merit Fv of 2.1×10 −10 C cm/J and Fm of 2.4×10 −8 C cm/J because of the relative low dielectric constant (er) of 35 and high pyroelectric coefficient (γ) of 4.0×10 −8 C/cm 2 K of the films. The pyroelectric infrared detector fabricated by the LiTaO3 thin film exhibits a voltage reponsivity Rv of 4584 V/W at 20 Hz and a high specific detectivity D ∗ of 4.23×10 7 cm Hz 1/2 / W at 100 Hz .
- Published
- 2003
36. Raman study on dislocation in high Al content AlxGa1−xN
- Author
-
Jiang Lijuan, Hang Xiao, Cuimei Wang, Haibo Yin, Xu Pan, Honggang Chen, Chenguang Feng, and Xiaoliang Wang
- Subjects
Materials science ,Photoluminescence ,Condensed matter physics ,Phonon ,Chemical vapor deposition ,Condensed Matter Physics ,Crystallographic defect ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Crystallography ,symbols ,Metalorganic vapour phase epitaxy ,Dislocation ,Raman spectroscopy ,Instrumentation ,Raman scattering - Abstract
The high Al content AlGaN epilayers have been obtained by metalorganic chemical vapor deposition (MOCVD), and the optical property has been investigated by photoluminescence (PL) spectroscopy. Longitudinal-optic (LO) phonon mode has been studied by Raman scattering. Further analysis shows that the edge dislocation is an important factor influencing optical quality of AlGaN epilayers, and it also shows that the correlation between the A 1 (LO) polar modes and the edge dislocation is intensive, which may be expected to become a characterization method of the related crystal defects.
- Published
- 2012
37. The influence of pressure on the growth of InAlN/AlN/GaN heterostructure
- Author
-
Hai-Yang Liu, Jianping Li, Jiang Lijuan, Honggang Chen, Yuhai Bi, Hongling Xiao, Cuimei Wang, Changqing Feng, and Xiaoliang Wang
- Subjects
Diffraction ,Materials science ,Atomic force microscopy ,business.industry ,chemistry.chemical_element ,Nanotechnology ,Heterojunction ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Stress (mechanics) ,chemistry ,Hall effect ,Torr ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,Instrumentation ,Indium - Abstract
The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation.
- Published
- 2012
38. Behavioural investigation of InN nanodots by surface topographies and phase images
- Author
-
Xiaoliang Wang, Qingwen Deng, Hong Chen, Cuimei Wang, Zhanguo Wang, Haibo Yin, Xun Hou, Hongling Xiao, Defeng Lin, and Jinmin Li
- Subjects
Number density ,Materials science ,Acoustics and Ultrasonics ,Condensed matter physics ,Quantum dot ,Annealing (metallurgy) ,Nanotechnology ,Nanodot ,Condensed Matter Physics ,Phase image ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
We employ surface topographies and phase images to investigate InN nanodots. The samples are annealed at 450, 500 and 550 □. The results reveal that the statistical distributions of number density and mean size depend on annealing ambient. The behaviours of thermal annealing between InN films and InN nanodots are distinguishable: the alloying process of InN and GaN not only occurs in InN platelets, but also in InN nanodots once the samples are annealed at the growth temperature of InN nanodots, while the main change in InN films is the decomposition of InN into In droplets and N2.
- Published
- 2011
39. Comparison of as-grown and annealed GaN/InGaN : Mg samples
- Author
-
Jiang Lijuan, Defeng Lin, Xiaoliang Wang, Xun Hou, Zhanguo Wang, Hong Chen, Hongling Xiao, Jinmin Li, Cuimei Wang, Haibo Yin, Chun Feng, and Qingwen Deng
- Subjects
Diffraction ,Photoluminescence ,Materials science ,Acoustics and Ultrasonics ,Band gap ,business.industry ,Doping ,Activation energy ,Condensed Matter Physics ,medicine.disease_cause ,Acceptor ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,medicine ,Optoelectronics ,business ,Ultraviolet ,Light-emitting diode - Abstract
Mg-doped InGaN was grown on unintentionally doped GaN layer, and Mg and defect behaviours in both GaN and InGaN : Mg were investigated through photoluminescence measurement at 7 K. Mg acceptor was found in unintentionally doped GaN after thermal annealing in N2 ambient, and Mg activation energy was estimated to be 200 meV and 110 meV for GaN and InGaN, respectively. Particularly, the ultraviolet band (3.0–3.2 eV) in the GaN layer was infrequently observed in the unannealed sample but quenched in the annealed sample; this band may be associated with oxygen-substituted nitrogen defects. Moreover, the measurement errors of photoluminescence and x-ray diffraction originated from strain were taken into account.
- Published
- 2011
40. An investigation on InxGa1−xN/GaN multiple quantum well solar cells
- Author
-
Qingwen Deng, Zhanguo Wang, Jinmin Li, Cuimei Wang, Qifeng Hou, Xiaoliang Wang, Haibo Yin, Hong Chen, Xun Hou, Hongling Xiao, and Defeng Lin
- Subjects
Physics ,Ideal (set theory) ,Acoustics and Ultrasonics ,business.industry ,Multiple quantum ,Energy conversion efficiency ,chemistry.chemical_element ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry ,law ,Solar cell ,Optoelectronics ,Quantum efficiency ,business ,Quantum well ,Indium ,Diode - Abstract
The conversion efficiency of In x Ga1−x N/GaN multiple quantum well solar cells is originally investigated in theory based on the ideal diode model and the ideal unity quantum well model. The results reveal that the conversion efficiency partially depends on the width of the quantum well and the thickness of the barrier region but is dominated by the number of quantum wells and indium content of In x Ga1−x N. The calculated results are found to be basically trustworthy by comparing with reported experimental results. An In0.15Ga0.85N/GaN multiple quantum well solar cell is successfully fabricated with a conversion efficiency of 0.2%. The main discrepancy between calculated and experimental results is the material quality and manufacturing technology which need to be improved.
- Published
- 2011
41. Influence of electric field on persistent photoconductivity in unintentionally doped n-type GaN
- Author
-
Qifeng Hou, Zhanguo Wang, Cuimei Wang, Cuibai Yang, Xiaoliang Wang, Jinmin Li, Hongling Xiao, Xun Hou, Haibo Yin, and Qingwen Deng
- Subjects
Condensed Matter::Materials Science ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Photoconductivity ,Electric field ,Doping ,Wide-bandgap semiconductor ,Coulomb blockade ,Electron ,Diode ,Dark current - Abstract
The influence of electric field on persistent photoconductivity in unintentionally doped n-GaN is investigated. It was found that under higher electric field the build-up course was slowed down while the decay course was accelerated. After a higher-voltage pulse, it was observed that the current dropped to a value lower than the dark current, and a current increase that lasted for thousands of seconds was observed. It is suggested that the above phenomena should be caused by the increase in capture rate of electron traps with electric field and are related to the Coulomb-repulsive characteristic of defects related to persistent photoconductivity.
- Published
- 2011
42. Deep levels in high resistivity GaN detected by thermally stimulated luminescence and first-principles calculations
- Author
-
Qifeng Hou, Yanqin Gai, Hongling Xiao, Xiaoliang Wang, Cuimei Wang, Jingbo Li, and Jinmin Li
- Subjects
Photoluminescence ,Acoustics and Ultrasonics ,Chemistry ,Doping ,Analytical chemistry ,Gallium nitride ,Condensed Matter Physics ,Thermoluminescence ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Electrical resistivity and conductivity ,Metalorganic vapour phase epitaxy ,Spectroscopy ,Luminescence - Abstract
Thermally stimulated luminescence spectroscopy has been applied to study the deep centres in unintentionally doped high resistivity GaN epilayers grown by the metal organic chemical vapour deposition method on c-sapphire substrates. Two trap states with activation energies of 0.12 and 0.62 eV are evaluated from two luminescence peaks at 141.9 and 294.7 K in the luminescence curve. Our spectroscopy measurement, in combination with more accurate first-principles studies, provided insights into the microscopic origin of these levels. Our investigations suggest that the lower level at 0.12 eV might originate from C-N, which behaves as a hole trap state; the deeper level at 0.62 eV can be correlated with V-Ga that corresponds to the yellow luminescence band observed in low-temperature photoluminescence spectra.
- Published
- 2009
43. Theoretical design and performance of InxGa1−xN two-junction solar cells
- Author
-
Cuimei Wang, Xiaoliang Wang, Cuibai Yang, Hongling Xiao, Jinmin Li, Qifeng Hou, Junxue Ran, Zhanguo Wang, and Xiaobin Zhang
- Subjects
Indium nitride ,Acoustics and Ultrasonics ,business.industry ,Band gap ,Irradiance ,Limiting ,Condensed Matter Physics ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Solar cell ,Optoelectronics ,business - Abstract
The efficiencies of InxGa1-xN two-junction solar cells are calculated with various bandgap combinations of subcells under AM1.5 global, AM1.5 direct and AM0 spectra. The influence of top-cell thickness on efficiency has been studied and the performance of InxGa1-xN cells for the maximum light concentration of various spectra has been evaluated. Under one-sun irradiance, the optimum efficiency is 35.1% for the AM1.5 global spectrum, with a bandgap combination of top/bottom cells as 1.74 eV/1.15 eV. And the limiting efficiency is 40.9% for the highest light concentration of the AM1.5 global spectrum, with the top/bottom cell bandgap as 1.72 eV/1.12 eV.
- Published
- 2008
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